Alternate mark inversion (AMI)
Alternate mark inversion (AMI) is a digital transmission technique in which binary values are sent by three voltage states.
- ‘0’ bits by a voltage of 0 volts.
- ‘1’ bits by a voltage of +V volts or -V volts alternatively
In AMI, zeros are represented by 01 during each bit cell
Ones are represented by 11 or 00, alternately, during each bit cell
A logical “0” is represented by 0 volts; A logical 0 is represented by no symbol
A logical 1 by pulses of alternating polarity.
- The alternating coding prevents the build-up of a D.C. voltage level down the cable.
- A logical “1” is represented by either a positive voltage or a negative voltage so that each alternate “1” is represented by a voltage level that is the opposite of that which represented the previous “1”.
The result is a digital waveform that has zero DC voltage on the line.
AMI (Alternate Mark Inversion) is a synchronous clock encoding technique which uses bipolar pulses to represent logical 1 value.
AMI Data Encoding
- Line-code type used on T1 and E1 circuits.
- AMI requires that the sending device maintain ones density. Ones density is not maintained independent of the data stream. Sometimes called binary coded alternate mark inversion
- Typically implemented as a RZ code
- Little or no DC content in signal
- Lacks transparency particularly during long sequences of binary ‘0’
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